The conventional fuel cell system of fuel recirculation type disclosed in the Japanese Laid-Open Patent Application Publication No. 2003-151588 is provided with a fuel cell to which a hydrogen gas as fuel and air as oxidant are respectively supplied for generating electricity, a fuel supply passage for supplying the above hydrogen gas to the fuel cell, a fuel recirculation passage for merging a hydrogen-containing off-gas as a unreacted fuel gas that has been discharged from the fuel cell at somewhere in the above fuel supply passage for re-circulating above hydrogen gas, a fuel pump for taking in the above hydrogen-containing off-gas to feed, and an ejector to inhale or taking in the above hydrogen-containing off-gas by making use of a negative pressure generated by the flow of the above hydrogen gas for merging with the hydrogen gas.
In the fuel cell system with a fuel recirculation type disclosed in Japanese Laid-Open Patent Application Publication No. 2003-151588, when the amount of supply of hydrogen gas is small, the velocity at the ejector nozzle is reduced, and due to the reduced Bernoulli effect, the hydrogen-containing off-gas is not sufficiently available for recirculation. Focusing on this phenomenon, at a low load condition with small supply or feed of hydrogen gas, a fuel pump is installed to take the hydrogen-containing off-gas in and subsequently deliver or feed.
However, in the above described configuration, in addition to providing the fuel pump, control of the fuel pump must be carried out so that the system becomes complicated with the difficulty to achieve system compactness.